Many aspects of the 3D-printing ecosystem are still very much wide-open research areas. Novel applications and technologies to improve 3D printing will likely be coming thick and fast for a long time. There is a classic cycle of technology adoption called the Gartner Hype Cycle ( www.gartner.com/en/research/methodologies/gartner-hype-cycle ). In this cycle, when a technology such as low-cost 3D printing comes along, lots of people get excited. There is much over-promising and under-delivering as people rush into what they think might be a multibillion-dollar market. Early adopters buy one because it is cool, not necessarily because they have a use for it. In the case of consumer 3D printing, that peak probably came in 2012 or 2013.
Then there is usually a fall-off and some consolidation. In the case of 3D printers, low-cost producers, many from China, made machines that did not meet unrealistic expectations for ease of use and typically did not provide any tech support that might have eased this. Gartner calls this the trough of disillusionment, and many 3D printer companies have indeed gone out of business in the last couple of years. The days are gone when everyone and their brother were putting up 3D printer ideas on Kickstarter.
Finally, we now seem to be in the more realistic growth period for 3D printing. Users understand that they need to know a bit about the process to get good results, and more sophisticated users are trying to push the boundaries. Some brave souls continue to start 3D printer companies. In this chapter, we look at research areas and advanced applications at the university and corporate research level. In Chapter 14, we speculate about where current students may find future careers in additive manufacturing.
Materials
Chapter 2 covers different materials that are available for 3D printing. As noted there, research in 3D printing is increasingly being driven by materials science research. There are vast arrays of filaments, resins, and powders (for industrial machines) available now, but that does not mean people are no longer doing research.
At the MIT Media Lab, Neri Oxman’s group ( www.media.mit.edu/people/neri/projects ) works with many novel materials, including glass. They have developed a process to 3D print large, notably transparent glass pieces.
Other groups at MIT (like the Tangible Media group, http://tangible.media.mit.edu/projects/ ) have also been working with 3D-printing materials that change shape after printing by being heated, for instance, so that they print flat and spring into interesting shapes after being heated, or perhaps inflated.
Printing in concrete is an active research area, too. The Center for Rapid Automated Fabrication Technologies (CRAFT, www.craft-usc.com ) at USC has been looking into 3D printing with concrete for quite a while. They have developed a technique called contour crafting , which lays up a thick, clay-like concrete followed by a blade that smooths away the layer lines. Here, too, developing concrete formulations that can be used this way has been a large part of the research effort. These printers make it possible to create concrete structures without using forms (with a pretty large external gantry). One application that has been proposed for the technology is to build many shelters quickly in the wake of natural disasters. Concrete is a good building material, but it needs reinforcement to make up for its low tensile strength. A number of companies and research groups have been developing ways to create buildings by extruding layers of concrete. They use different methods to add reinforcement to the structures.
These examples, of course, are only a few of the many programs at universities around the world. If you are interested in a particular application or material, searching the peer-reviewed literature will likely yield some results.
Printing Metal
Printing directly in metal is a difficult industrial process and not likely to occur in homes or offices anytime soon. Some companies we talk about in Chapter 2’s “Advanced Filaments” section have come out with metal-filled filament that embeds metal in plastic. The mixture is used to print, and then the plastic is baked out. However, if you are moving to an industrial scale, 3D printed metal parts are really coming into their own.
Direct printing of metal usually involves metal powder that is fused by a laser or with some sort of binder (which also needs to be baked out). The challenge is that metal powder is dangerous and difficult to work with, and is even prone to explosions. For that reason, most metal 3D printers operate in an inert gas atmosphere, like argon. The materials handling procedures of powder-based metal 3D printers require significant facilities investments.
Titanium bone replacements are printed in a fine lattice pattern so that bone will grow into them, a process called osseointegration .
“Lightweighted” aerospace structures are made very strong but light by creating complex parts which have lattice-like structures only where they need to be to carry a load, and open space where they do not.
Complex parts can be made that combine dozens or even hundreds of previous components, saving assembly time and improving reliability.
More and more alloys are available for 3D printing, too, from steel to aluminum alloys and titanium.
Analyzing Parts
As we have said repeatedly in this book, 3D printers are robots that are really not all that sophisticated, and that may be using materials that have very poorly characterized engineering properties. At this level of sophistication, modeling the stresses experienced by a 3D printed part is challenging, other than by destructively testing an exact replica. This may change over time, but it is one of the factors limiting applications of small printers for tasks that require analyzing stresses on the part in software first.
Industrial printers are in another category entirely. Systems like the large metal printers need sophisticated process control. To complicate matters, if one is designing a part for a critical use, software is needed to model the loads on that part. At the moment, many of the standard engineering software packages that engineers use to design parts cannot handle 3D printed parts well or at all. As discussed in Chapter 9, 3D prints can be stronger in some directions than others, particularly ones that use filament. Printer manufacturer 3D Systems, which has many printers in this market, handles this by selling integrated design and printer control software, with tight specifications for materials.
Generative design software, which creates possible designs for parts based on requirements for them, is evolving as a way to help humans design complex parts optimized for 3D printing—for example, parts with lots of load-bearing latticework. Autodesk is exploring this idea, as described at www.autodesk.com/solutions/generative-design .
Printing Food
3D printed food was a hyped application a few years ago, but this enthusiasm has since been tempered. The reality is that 3D printing is slow (compared to industrial throughput), and managing finicky temperature ranges while making printers food-safe is a challenge. To be food-safe, printers need to have everything that touches food be sterilizable and be made of food-safe materials. To solve these issues, most food printers use some sort of syringe-like device to extrude a paste.
Variety is limited though, because most food printing does not involve the actual programmatic creation or mixing of ingredients, but simply involves extruding these mixtures into predetermined locations (something that is already commonplace in the creation of packaged food). However, printing pieces that can be used to make molds is a promising area of development for customizing the shapes of food products, rather than their compositions.
There are niche printers for chocolate (for example, http://chocedge.com ). There are also “3D printers” that make pancakes ( www.pancakebot.com ), but they are really just drawing in 2D.
Bioprinting
Specialized biological printers (to make human organs, for example) are called bioprinters , and we touched on these in Chapter 2. They have similar design constraints to food printers and are also often syringe-based systems. Bioprinters lay down a medium (usually some kind of gel, like alginate) that contains live cells. Cellink ( https://cellink.com ) has been developing “bioinks” to facilitate other types of structures, and has a multi-head printer that also includes capabilities such as UV sterilization. Different heads can be used to lay down different types of materials that require cooling, say, or heating.
Bioprinters have garnered a lot of press lately, and here the 3D printer part is relatively easy. Learning how to grow tissues that can be accepted by the human body will be the hard part going forward.
Custom Equipment and Prototypes
The next chapter discusses short-run manufacturing and prototyping more generally. In the university environment, 3D printing can be a very cost-effective way to create lab equipment. This is particularly true when no good existing equipment will serve the desired purpose.
We were part of an effort a few years ago to help University of California, Riverside, entomology researchers in Richard Stouthamer’s lab design a 3D-printable “emergence trap” for the polyphagous shothole borer (PSHB).
PSHB beetles bore into a tree and deposit a fungus and ultimately eggs for the next generation. The researchers wanted to create a trap that would attach to a tree and catch some of the beetles and the fungus for study, and see how many beetles and their offspring were emerging from the holes they had bored into the trees. 3D printing allowed the scientists to iterate designs as they learned more about what would work, and to have exactly what they wanted.
Note
If you want to read the details of the bug trap case study, it has been published in this scientific journal article: Daniel Berry, Roger D. Selby, Joan C. Horvath, Rich H. Cameron, Diego Porqueras, Richard Stouthamer (February, 2016), “A Modular System of 3D Printed Emergence Traps for Studying the Biology of Shot Hole Borers and Other Scolytinae.” Journal of Economic Entomology, DOI: 10.1093/jee/tov407.
Another area where 3D printing has made a difference is in experiments that require managing small amounts of fluid, sometimes called millifluidics , to distinguish it from the even-smaller microfluidics. These applications require custom tiny flow paths to study various fluid properties. For examples, try searching on “millifluidics 3D printing” in the Public Library of Science (PLOS) open-access journals, http://collections.plos.org , for recent work in this space.
Standards
One of the challenges in using 3D printed parts is that filament’s mechanical properties can vary widely, even with the colors of a manufacturer’s PLA, for instance. For filament-printed parts especially, the part geometry and the relative direction of forces to layer lines matters a lot. Resin print properties can depend both on the resin’s mechanical properties and on how well the curing process followed specifications. Parts that require finishing or baking out have uncertainties introduced in those steps.
Joshua Pearce’s group at Michigan Technological University has been publishing about their attempts to get realistic numbers for some of these key mechanical and chemical properties. Many papers are linked in their Appropedia wiki at www.appropedia.org/Pearce_publications_in_materials_science_and_engineering .
The American National Standards Institute (ANSI) and various collaborators are working on a standard: www.ansi.org/standards_activities/standards_boards_panels/amsc/ .
ASTM has standards, including those for specific metals, at www.astm.org/Standards/additive-manufacturing-technology-standards.html .
There is a lot of work to do here, and thorough characterizations of materials and geometries will be a research effort for some time to come.
Summary
Researchers at the university level have many options to improve the 3D-printing process: by creating new materials, finding novel ways to use existing ones, and finding new applications. There is still much work to be done to make 3D printing easier to use, and to make the physical and chemical properties of 3D prints more consistent and reliable for demanding applications. Meanwhile, scientists can take advantage of the technology to create custom equipment that can let them explore frontiers more cheaply and creatively than might have seemed possible before the ubiquity of low-cost printers.